Conventionally, a combined heat exchanger is known, which is configured to be capable of performing heat exchange among three kinds of fluids. For example, in Patent Document 1, a heat exchanger is disclosed, which is configured to be capable of performing heat exchange between refrigerant of a refrigeration cycle device and outdoor air (outside air), and performing heat exchange between the refrigerant and coolant that cools an engine.
Specifically, the heat exchanger of Patent Document 1 includes multiple refrigerant tubes that are lamination-arranged, and both end portions of the refrigerant tubes are connected to refrigerant tanks that collect and distribute refrigerant. The heat exchanger further includes heat pipes arranged between the lamination-arranged refrigerant tubes, and one end portions of the heat pipes are connected to a coolant tank through which coolant flows. Further, heat-exchange promoting fins are arranged in air passages provided between the refrigerant tubes and the heat pipes.
When the refrigeration cycle device is operated, refrigerant evaporates by absorbing heat of outside air and heat of coolant (i.e., waste heat of the engine), and frost formation in the heat exchanger is limited by using the waste heat of the engine transmitted through the heat pipes as a heat source.